RE: OS 70 Ultimate w/pump
The OS 70 Ultimate has been discontinued by Tower
When first introduced it had a very checkered success whereby Tower Took it off the market
After more than a year, Tower again offered them for sale and the engine performed better with some improvements and tuning instructions
The problem area tended to center around the combined Regulator/carb which is no longer available as a spare part
The carb was a slide valve type rather than having a rotary barrel as in most model airplane engines
By the time the engine was running better, other brands including newer OS models had arrived on the market to have more power